Vast emptiness of silent glory

For hundreds of years, people have been concerned that the world's deserts are encroaching insidiously on productive land lying on their margins. The concept of "post-glacial progressive desiccation" was widely adopted, particularly in Africa and India. In 1949 a French botanist, Andre Aubreville, invented "desertification" as a term to describe the change of productive land into desert. Since that time, there has been extended debate as to what the term really means, whether human actions or climate change are responsible for desertification, the speed at which the process is occurring, and its significance for human welfare.

At one extreme there are those who believe that substantial tracts of the world's deserts are man-made and that desertification is a problem of a magnitude that makes it one of the great issues of the age. At the other extreme there are those who argue that desertification is a myth and that there is little high-quality data to substantiate it.

The reality is that in some parts of the world desert margins have become much degraded; in some areas, such as the Sahel, droughts have become more pervasive in recent decades; but in other areas desert margins have been proven to be resilient to various pressures (natural and anthropogenic), as have their human inhabitants. The study of desertification in part involves a consideration of biogeophysical processes such as dune reactivation, dust-storm generation, gully formation, sheet erosion, groundwater depletion, salt accumulation and vegetation degradation. However, it also involves a consideration of social, political and economic issues, including sustainability, vulnerability and carrying capacity. In short, desertification is a devilishly complex problem beset by a severe shortage of reliable quantitative data.

The purpose of Helmut Geist's book is to use data from 132 subnational case studies to generate a general understanding of the proximate causes and underlying driving forces of desertification and its progression. The overall conclusion is that the key concept should be "multiplicity". The studies reveal multiple uses of the land with multiple environmental histories, multiple agents of change, multiple ties between people and land, and multiple responses to change. They also suggest that in some areas desertification is episodic, in others it is progressing, in still others it is reversing.

Geist's book is modest in format, serious, unillustrated, full of long tables of data, heavily referenced and, ultimately, sensible in its conclusions. It is an antidote to some of the uninformed hand-waving that has taken place in the past. It is useful not only because of its analyses, but also because it has a good review of some of the uncertainties, advances and debates in desertification research, and gives indications as to how indicators of desertification can be improved.

By contrast, Philippe Bourseiller's book is in a very large format, extremely heavy, extensively illustrated and has little text. Its basic message is that the Sahara Desert is extraordinarily beautiful. This might come as something of a surprise to those who have seen the comments of some 19th-century writers, many of whom found the Sahara repellent. Elisee Reclus was especially dismissive of its attractions: "Even the flea will not venture into these dreadful regions. The intense radiation of the enormous white or red surface of the desert dazzles the eyes; in the blinding light every object appears to be clothed with a sombre and preternatural tint. Occasionally, the traveller, when sitting upon his camel, is seized with the rgle, a kind of brain fever, which causes him to see the most fantastical objects in his delirious dreams. Even those who retain the entire possession of their faculties and clearness of their vision, are beset by distant mirages. When the wind blows hard, the traveller's body is beaten by grains of sand, which penetrate even through his clothes and prick like needles."

The photographs in the book, in full colour, cover a range of territory from Mauritania in the west to the White Oasis of Farafra in the east. The subjects range from human to natural, with detailed captions at the end of the book. Mercifully, there are not too many photos of camels and palm trees. Those of the sandstone landscapes of Ennedi are spectacularly beautiful and give a picture of some very remote districts in the heart of the Sahara.

Almost hidden away within the photographs are some sections of text, written by French experts - Edmond Bernus, Monique Brandily, Jean-Francois Chaix, Marceau Gast, Malika Hachid and Yvette Veyret - and of respectable quality. These deal with such issues as climate change, the formation of dunes and other geomorphological features, the archaeological history of the region, nomads and nomadism and so on. They are perfectly good little essays, but I doubt that anyone will be persuaded to buy the book because of them.

It is the 174 pictures taken by Bourseiller that are the attraction. And in one of the chapters, Chaix, writing of Ennedi, gives a clue as to why the photographs are so good: "Not one but a hundred Monument Valleys stretch as far as the eye can see: monoliths such as only the great open spaces can produce, their piles driven deep into the sand that beats against their enormous pedestals. Silent glory spreads out majestically before us, a labyrinth of regal avenues through which we could never have found our way without guides. We are intoxicated by this geology. There may be only seven wonders of the world, but the Sahara contains enough wonders to dazzle seven worlds."

Andrew Goudie is master of St Cross College, Oxford, and author of Great Warm Deserts of the World.